Method for freezing products by direct-contact with an evaporating freezing agent

ABSTRACT

A novel method and apparatus for quickly freezing food products by a direct contact with an evaporating liquid freezing agent with a minimum of loss of the freezing agent comprising feeding the food into a freezing vessel; substantially removing all the air in this freezing vessel by purging with vapors of the freezing agent; freezing of the food by means of direct contact with the liquid freezing agent; purging the vessel of freezing agent vapor by means of air and removing the frozen food product.

United States Patent [191 Romijn Oct. 16, 1973 [54] METHOD FOR FREEZINGPRODUCTS BY 3.007.319 11/1961 Ogden l; (12/64 DIRECT CONTACT WITH AN3,479,833 11/1969 Waldin 62/63 QRATI QFREEZWQA Inventor JohannesOerardus RomijnQ 7 S Hertogenb osch Nthefiands Assignee: GrassosKoninklijke b lachinen- V fabrieken, N.V.

[22] Filed: Jan. 31,1972

[21] Appl. No.: 222,082

[30] Foreign Application Priority Data Feb. 2, 1971 Netherlands 7101362[52] US. Cl. 62/64, 62/85 [51] Int. Cl. F25d 17/02 [58] Field of Search62/63, 64, 85

[56] 7 References Cited UNITED STATES PATENTS 2,502,527 4/1950 McFarlan62/85 X Primary Examiner-Meyer Perlin Assistant Examiner-Ronald C.Capossela Attorney-Nathaniel L. Leek A novel method and apparatus forquickly freezing food products by a direct contact yvith an evaporatingliquid freezing agent with a minimum of loss of the freezing agentcomprising feeding the food into a freezing vessel; substantiallyremoving all the air in this freezing vessel by purging with vapors ofthe freezing agent; freezing of the food by means of direct contact withthe liquid freezing agent; purging-the vessel of freezing agent vapor bymeans of air and removing the frozen food product.

ABSTRACT 11 Claims, 1 Drawing Figure METHOD FOR FREEZING PRODUCTS 'BYDIRECT-CONTACT WITH AN EVAPORATING FREEZING AGENT It is known fromtheU.S. Pat. No. 3,368,363, that food can be very quicklyfrozen byimmersing it in, or sprinkling it with a liquid having a boiling pointbelow the freezing point of the food, i.e., between 5 and -50C. Inconsequence of the exceptionally" good heattransfer between theebullient liquid andthe food and in consequence of the low temperatureof the liquid, heatis being withdrawn so quicklythat many food will befrozen within a couple of minutes.

In consequenceof the fast freezing a conserved product is formed whichafter'having been thawed and=prepared, deviates much less from a freshproduct than a product which has been frozen more slowly.

By the simple and direct method of heat-withdrawal by meansof immersionor sprinkling in contact with an ebullient liquid, it is tobeexpectedthat'the equipment destined for this freezing will also besimpler than with other less directmethods.

Moreover it is to be expected that the consumption of energy of thecooling plant for the withdrawal of heat will be lower.

If the ebullient liquid, with which the food is being brought intocontact, is harmless for the food and in the existing smallconcentrations in the food is also harmless for the health of manandanimal, then thismethod is useful. One of the substances which meets allthe requirements mentioned above, is pure dichlorodifluoromethane,indicated in trade and in the cooling technics mostly as R12.

With low temperatures this liquid is chemically'stable and nothygroscopic.

Another important benefit of this liquid is, that it does not attachitself much to the food with which it is brought into contact, so thatit appears after freezing, that per unit of weight of frozen food thequantity of R12 still existing in it, is mostly smaller than one tenthousandth unit of weight.

In the US. Pat. No. 3,368,363 an apparatus and a method is described inwhich, by means of the above mentioned liquid refrigerant R12 (C.C-l,F,,diclorodifluoro-methane), food is being frozen. With thismethodattention is paid to the prevention of the loss of vapour of thisliquid. This is necessary because the substance in its pure form, inwhich it is suitable for this method is costly. According to thedescription in the above mentioned patent specification it isthuspossible to reduce the loss of vapour to two parts by weight per 100parts of the food frozen in the apparatus. According to this method theescape of vapour is being reduced by locks, as well as the penetrationof atmospheric air into the apparatus Besides the vapour together withthe air, the water vapour, the carbon dioxide and other volatilesubstances existing in it is being compressed to a pressure in which thevapour in a water-cooled heat exchanger will condense and afterwards bebrought back to the freezing apparatus. Care is being taken that thenon-condensed substances are separated from the liquid and aredischarged to the atmosphere in such a waythat only little of the liquidrefrigerant (R12) is lost as vapour.

The described method is based on generally known methods in the coolingtechnics and usable herein, but this method is complicated owing to themany mechanical aids and appliances required for that purpose. It is notquite reliable owing to the considerableimpurites being carried alongwith the vapour stream, especially water vapour, and which may causechokings in narrow passages at a low temperature and it is above all notvery active because much air penetrates into the apparatus throughthelocks and vapour escapes and also because when the liquid and thenon-condensed substances are being separated a large quantity of vapouris carried along with the non-condensed substances.

Besides, an objection to this method is, that the vapour together withthe air and other vapours is being compressed and as a result thereofobtains a temperaturefar above the atmospheric temperature.

The pure compound C Cl F can under these circumstances, in contact withmetals (and in the presence of water vapour, air, carbon dioxide andother volatile substances) be transformed in a small degree intosubstances which are very harmful to the health.

The invention described below, avoids all the above mentioned objectionsand means an important improvement of the applicability of the methodmentioned before of the freezing of food.

The method according to this invention is simple, does not give causefor chokings, it is very efficient, even sothat'the loss of vapour'canbe simply reduced to l 10 parts by weight per hundred parts by weight offrozen food. Moreover the vapour is not compressed considerably inanypart of the process, while the maximal temperature falling to the vapourin any part of that process, is lower than the temperature of the foodbrought in, which is usually lower than that of the atmosphere.

The method according tothis invention consists of the fact, that thevessel, the apparatus or the locks in which or through which the food isbeing brought in and in which accordingly air is present together withall its components, is flushed with the vapour of the ebullient freezingliquid, as a result of which the air is expelled and rarefied, to suchan extent that the partial pressure of the air has fallen to a valuewhereby the action of the freezing apparatus is not reduced, forinstance to about 0.05 bar, that is 5/100 of the total pres sure in't hevessel or freezing apparatus or lower.

When the frozen product leaves the freezing apparatus, the vessel or thelock contains only the frozen product and the vapour of the freezingliquid. The vapour is expelledfrom the vessel or the lock by flushingwith air or an other suitable gas, to such an extent that only a smallquantity of vapour will stay behind. In emptying the vessel or the lockthe remaining vapour will be lost almost completely.

With the method according to this invention this quantity can be simplyreduced to l/ 10 parts by weight per parts by weight of frozen food.

In doing so there is no need of complicated mechanical constructionssuch as blowing devices, compressors and vacuum airpumps.

During the freezing of the food the vapour formed by the boiling processof the liquid, is condensed on a cold surface, consisting of cooledpipes or plates. This surface can be cooled by the usual industrialcooling plants, which may be chosen in such a way as to achieve the bestpossible results. With the method according to this inventioncondensation of the vapour of the freezing liquid on the cooled surfaceis scarcely hampered by the presence of non-conde'nsable gases or byreduction of the vapour tension and accordingly of the condensationtemperature of the vapour as a result of strong rarefying bynon-condensable gases.

Therefore the temperature of the cooled surface can almost be equal tothat of the ebullient freezingliquid or just a little bit lower, forinstance 1 C. For the benefit or condensation the vapour can be movedstrongly by suitable means; besides it is possible to stimulatecondensation of the vapour by sprinkling part of the liquid over thecooled surface, as a result of which the liquids gets supercooled andthe vapour can also condense on the falling drops. During the sprinklingwith the vapour and the air a mixture of vapour and air is beingdischarged from the vessel or the locks of the freezing apparatus. Thismixture should be actively separated before the air can escape to theatmosphere.

According to the method of this invention the mixture is led through avessel or column, which is filled with part of the freezing liquid at atemperature between 60 and 120 C, or through a heat exchanger which isbeing kept at said low temperature. The vessel or the column ispreferred, because owing to close contact in there between the mixtureof vapour and air, and the cold liquid, the vapour will for the greaterpart condense and water and other condensable volatile components of themixture will stay behind in the liquid and admixtures, which do notdissolve in the liquid can be easily be removed, while nevertheless inthe heat exchanger vapour and condensable admixtures are condensed, butan accumulation of admixtures, which do not dissolve in the liquid caneasily cause chokings, which is one of the objections to the methodaccording to U.S. Pat. No. 3,368,363.

The mixture coming out of the column or the vessel contains all the airand such a quantity of vapour as corresponds with the vapour tension atthe temperature of the column. With the R12 freezing liquid the vapourtension is: at 60 C about 0.23 bar and the specific volumne of thevapour 0.63 m /kg; at 90C about 0.03 bar, and the specific volume 4 mlkg; at l20 C about 0.002 bar and the specific volume about 30 m lkg.

That means that with each m of air coming out of the column or thevessel, resp. about 1.5 kg R12 at 60" C, 0.25 kg R12 at 90 C and 0.03kg. R12 at l20 C columntemperature should be lost with the air.

For freezing 1,000 kg of food a vessel is needed of about 2 m so thatabout 1 in will be taken in by the art.

For washing away and rarefying the air, 2 to 5 m of vapour are needed.In the same way, 2 to 5 m of air are needed for washing away andrarefying the vapour to take care that the quantity of vapour leavingthe vessel or the lock together with the frozen food, is smaller than 1kg per 1,000 kg. of product.

Consequently l m of air passes through the column together with the foodand 2 to 5 m of air needed to wash away the vapour; total therefore 3 to6 in per 1,000 kg of food.

As a result of this the loss of vapour at a columntemperature of 60 Cwould amount to max. 9 kg. per 1,000 kg and at a columntemperature of lC. 0.1 kg per 1,000 kg plus 0.1kg/l,000 kg owing to loss of vapour fromthe lock or the vessel. In comparison with the 40 kg per 1,000 kgaccording to the method described in the U.S. Pat. No. 3,368,363, thismeans, especially at temperature lower than 60 C, an important increaseof the action of the method in order to recover the vapour. A methodwhere, apart from some shut off valves and an air pump of littlecapacity and difference of pressure, no moving parts are present in thevapour lines.

The condensed liquid can be brought back into the freezing apparatus bymeans of evaporation at for instance 1 bar, while the boiling point isabout 30 C, and all impurities will stay behind in the column. By meansof the choice of the contents of the column, this action may, ifnecessary, be reduced to for instance once a day or even once a week,but it may be performed continuously as well.

A refinement of the above described method according to this inventionis the following:

The air which is present in the vessel or the lock when the food isbrought in, is expelled by the vapour as described above and for thegreater part stripped of the vapour and of the admixtures in the columnwith cold liquid and afterwards temporarily assembled in a balloon or asmall gas holder.

The air is allowed to have a rather high vapour concentration forinstance up to a vapour tension of 0.5 bars, as a result of which theliquid in the column, when the vapour therein is condensing, only has tobe cooled up to 45 C. As a result of this a smaller cooling plant of thecolumn will suffice than according to the method described earlier.

With a circulating pump for the air it is now possible, during theperiod that the lock does not work or during the freezing period in thevessel, to lead the air through the column again and again, while thecooling plant of the column continues working and as a result of whichreduces the temperature of the liquid in the column to for instance 60or C, in consequence whereof the vapour tension of the liquidrefrigerant falls to below 0.23 bar.

In case the food has to leave the vessel or the lock, the air is heldout of the balloon or the gas holder with the airpump through the vesselor the lock, while the vapour in the vessel or the lock is being washedaway and rarefied.

The mixture coming out of the vessel or the lock, is led through thecolumn till the vapour tension of the vapour in the lock or the vesselis almost equal to the vapour tension of the liquid in the column. Thatis to say at 60 C in the column almost equal to 0.23 bar or at C in thecolumn up to 0.03 bar, accordingly as the recovery having to be lessactive or active.

When this low vapour tension has been reached, the food leaves theapparatus together with the air and a small quantity of vapour.

The volume of the air per 1,000 kg. of food, passing through thefreezing apparatus with this improved method, and is lost in theatmosphere, is now reduced to not more than about 1 m, as a result ofwhich the loss of vapour is reduced to about 1.5 kg per 1,000 kg offood, the columntemperature being 60 C and to 0.25kg per 1,000 kg offood, the final temperature in the column being 90 C.

The invention is illustrated further by the drawing.

The liquid side of a condenser 6 for the vapour of the freezing agenthas been connected with a freezing vessel l, which may be provided withlocks (not shown in the drawing) for the introduction and discharge ofthe food, via a line 16, 17, in which line l6, 17 there is a liquidcondensate pump 9 and a shut off valve 4. The freezing vessel 1 isconnected on the vapour side of the condenser 6 via a line 18 with ashut off valve 3 and a vapour ventilator 10. The cooling plant for thecondenser6 has been given the reference number 15.

The freezing vessel 1 is connected with a column 7,

via a line 19,20, provided with a shut off valve 2 ancl a line 21, 22,23, provided with an air pump 11 and a shut off valve 5; the coolingjacket 24 is being cooled via a cooling plant 13, which is connectedwith a condenser 14. The cooling spiral 25 of the condenser 14 isconnected with the freezing medium in the condenser 6 via lines 26, 27and line 16. A balloon or gasholder 8 is connected with the lines'2l,22, while line 28, provided with a shut off valve 12 connects the lines19, 20 and 22, 23.

An example of the method for the recovery of the vapour according to theinvention is the following:

1,000 kg of food with a contents of 2 m are being brought into thefreezing vessel 1. After closing, the vessel contains 1,000 liter ofair. Now about'5,000 liter of vapour. is being blown rapidly throughthevessel, for instance by bringing from the condenser 6 for the vapour 30kg. of liquid in the vessel 1 via the line l6, 17 through the pump 9with the shut off valve 4 being opened. 4

This liquid evaporates very quickly when it is brought into contact withthe still warm food and procures at 1 bar absolute pressure about 5,000liter of vapour. As a result of this the air is being expelled andrarefied to a partial airpressure of 5/100 to H100 bar in vessel 1,while a mixture of 24 kg of vapour and about 1.25 kg. of air flowsthrough line 19, 20to column 7 with the shut off valve 2. being openedand about 6 kg. of vapour stays behind in vessel 1.

The volume of air with part of the vapour amounts to 0.7 to 1.0 m afterpassing of the cooled column 7, dependent on the temperature and thepressure in the balloon or gasholder 8.

When after a few seconds the mixture has flown through this column 7 tothe balloon or gasholder 8 the shut off valve 2 is being closed and theshut off valves 3 and 4, which connect vessel 1 with the cooled vapourcondenser 6, open, while the liquid circulating pump9 and the vapourventilator 10 become effective.

Dependent on the temperature of the cooled condenser 6 the temperatureof the ebullient liquid in vessel 1 will be 10 to 40 C.

This temperature is chosen according to the requirements, which havebeen put to the freezing speed of the food. The product freezescompletely in 3 to 90 minutes. Meanwhile the airpump ll circulates themixture of air and vapour through column 7 via the lines 21, 22, 28 andwhile the shut off valve 12 is open, while the continuously workingcooling plant 13 of column 7 will reduce the temperature of the liquidin column 7 to 60 to 90 C. The food being completely frozen, the shutoff valves 3 and 4 between vessel 1 and condenser 6 are closed, pump 9and ventilator 10 are brought to a standstill, the shut off valves 2 and5 are opened and the shut off valve 12 is closed.

In the vessel 1 there is still about 6 kg of vapour left, so about 1/5part of the quantity needed when the air was expelled from vessel 1.

When the airpump 11 has circulated 3,000 to 5,000 liter of air with thelow vapour tension of the liquid, then the vapour tension in vessel 1has fallen to 0.05 to 0.01 bar above the vapour tension in the balloonor the gasholder 8, which at 60 C in column 7 is equal to tension invessel 1 is than 0.28 to 0.04 bar dependent on the circulated quantityof air and the temperature of the liquid in column 7'. Both quantitiesmay be chosen at liberty according to the requirements being put to theactivity of there'covery of vapour according to the process of workingof the invention and they afford the opportunity of choosing theactivity of recovery.

The vapour still left in vessel 1, will be lost if the shut off valves 2and 5 are being closed and the food leaves the vessel. With a vapourtension of 0.28 bar in the vessel this amounts to appr. 1.7 Kg, with avapour tension of 0.04 bar this will be 0.24 kg of vapour, per 1,000 kgfrozen food, so that the loss may be reduced to less than 0.1 kg/100 kgof food.

According to this method about kg of vapour must be'condensed in column7 by way of contact with the cold liquid, furthermore about 1.25 kg ofair have to be cooled and one has to take account of some heat supplyowing to conduction, as a result of which per 1,000 kg of product 1,500to 2,500 kcal will have to be discharged in total at column temperatures7 between 40 and -90 C.

.For the freezing of the food there will be necessary per 1,000 kg,dependenton its nature and its startingand final temperature, 75,000 to120,000 kcal, which will have to be discharged by the cooling plant 15of the condenser 6 for the damp of the liquid refrigerant.

The cooling capacity for column 7 amounts therefore to 2.5 to 3.5percent of that for the condenser 6.

For cooling plant 13 of column 7 a cryogenerator of a well-knownconstruction or a simple compression 0.23 bar and at C is about 0.03bar. So the vapour cooling plant of small capacity with a suitablefreezing medium will be considered, for instance R22 R13 or Freon 12Bromine l, with which the condenser 14 is cooled by the evaporatingfreezing medium of the cooling plant 15 for the condenser 6 of thevapour or by part of theliquid from the condenser 6.

The cooling plant 13 of column 7 will, at a lowest temperature in column7 of 60 C, work at an average evaporating temperature of about 50 C andat a lowest temperature in column 7 of 90 C, at an average evaporatingtemperature of about 60 C.

An important characteristic of theprocess of working as describedearlier is, that in vessel 1 or in the locks which are connectedwith thefreezing apparatus for the introduction or discharge of the food, thepressure is almost equal to the atmospheric pressure, as a result ofwhich it is possible to freeze food, which might deform or become unfitfor use owing to changes of pressure, such as many frothy foods, forinstance ice-cream, whipped cream, pastry etc. by bringing them intocontact with an ebullient freezant.

What we claim is:

1. A process for freezing food products by direct contact with anevaporating liquid freezing agent in a freezing vessel comprisingplacing said food products in said vessel, closing said vessel, purgingsaid closed vessel in order to substantially remove the air in saidfreezing vessel by introducing vapors of said liquid freezing agent toform a first freezing agent vapor-air mixture, recovering the freezingagent from said first freezing agent vapor-air mixture by passing saidfirst freezing agent vapor-air mixture along a cold surface so that saidfreezing agent vapor condenses, freezing said food by direct contactwith said liquid freezing agent forming freezing agent vapors, purgingsaid closed freezing vessel with air to substantially remove saidfreezing agent vapor and form a second freezing agent vapor-air mixture,recovering said freezing agent from said second freezing agent vapor-airmixture by passing said second freezing agent vapor-air mixture alongsaid cold surface so that said freezing agent vapor condenses, openingsaid freezing vessel and removing said food from said vessel.

2. The process of claim 1 which additionally comprises the step ofstoring the air from said first freezing agent vapor-air mixturesubsequent to the removal of said freezing agent vapor by said coldsurface and reutilizing said stored air for purging said freezing agentto form said second freezing agent vapor-air mixture.

3. The process of claim 1 wherein the recovery of said freezing agentfrom said first freezing agent vaporair mixture is conductedsimultaneously with the freezing of said food by direct contact withsaid liquid freezing agent, said recovery comprising continuouslycirculating said first freezing agent vapor air mixture along said coldsurface in order to substantially remove the freezing agent from saidfirst freezing agent vapor-air mixture.

4. The process of claim 3 which additionally comprises the step ofstoring the air from said first freezing agent vapor-air mixturesubsequent to the removal of said freezing agent vapor by said coldsurface and reutilizing said stored air for purging said freezing agentto form said second freezing agent vapor-air mixture.

5. The process of claim 1 wherein the temperature of said cold surfaceis lower than the final temperature of the product to be frozen.

6. The process of claim 5 wherein said lower temperature is generated bya compressor cooling plant having a condenser cooled by a main coolingplant.

7. The process of claim 5 wherein the lower temperature is generated bya cryogenator.

8. The process of claim 1 wherein the pressure within the freezingvessel is essentially equal to atmospheric pressure.

9. The process of claim 8 wherein the partial pressure of the air in thefreezing chamber during freezing is lower than 0.05 bars.

10. The process of claim 1 wherein the vapor pressure of the vapor ofthe freezing agent which is present in the said freezing vessel when thefrozen products are removed is lower than 0.28 bars.

11. The process of claim 10 wherein the partial pressure is lower than0.05 bars.

1. A process for freezing food products by direct contact with anevaporating liquid freezing agent in a freezing vessel comprisingplacing said food products in said vessel, closing said vessel, purgingsaid closed vessel in order to substantially remove the air in saidfreezing vessel by introducing vapors of said liquid freezing agent toform a first freezing agent vaporair mixture, recovering the freezingagent from said first freezing agent vapor-air mixture by passing saidfirst freezing agent vapor-air mixture along a cold surface so that saidfreezing agent vapor condenses, freezing said food by direct contactwith said liquid freezing agent forming freezing agent vapors, purgingsaid closed freezing vessel with air to substantially remove saidfreezing agent vapor and form a second freezing agent vapor-air mixture,recovering said freezing agent from said second freezing agent vapor-airmixture by passing said second freezing agent vapor-air mixture alongsaid cold surface so that said freezing agent vapor condenses, openingsaid freezing vessel and removing said food from said vessel.
 2. Theprocess of claim 1 which additionally comprises the step of storing theair from said first freezing agent vapor-air mixture subsequent to theremoval of said freezing agent vapor by said cold surface andreutilizing said stored air for purging said freezing agent to form saidsecond freezing agent vapor-air mixture.
 3. The process of claim 1wherein the recovery of said freezing agent from said first freezingagent vapor-air mixture is conducted simultaneously with the freezing ofsaid food by direct contact with said liquid freezing agent, saidrecovery comprising continuously circulating said first freezing agentvapor air mixture along said cold surface in order to substantiallyremove the freezing agent from said First freezing agent vapor-airmixture.
 4. The process of claim 3 which additionally comprises the stepof storing the air from said first freezing agent vapor-air mixturesubsequent to the removal of said freezing agent vapor by said coldsurface and reutilizing said stored air for purging said freezing agentto form said second freezing agent vapor-air mixture.
 5. The process ofclaim 1 wherein the temperature of said cold surface is lower than thefinal temperature of the product to be frozen.
 6. The process of claim 5wherein said lower temperature is generated by a compressor coolingplant having a condenser cooled by a main cooling plant.
 7. The processof claim 5 wherein the lower temperature is generated by a cryogenator.8. The process of claim 1 wherein the pressure within the freezingvessel is essentially equal to atmospheric pressure.
 9. The process ofclaim 8 wherein the partial pressure of the air in the freezing chamberduring freezing is lower than 0.05 bars.
 10. The process of claim 1wherein the vapor pressure of the vapor of the freezing agent which ispresent in the said freezing vessel when the frozen products are removedis lower than 0.28 bars.
 11. The process of claim 10 wherein the partialpressure is lower than 0.05 bars.